Attention has been paid to silicon photonics that is a technique of integrating silicon optical circuits on a silicon chip. In the silicon photonics, there are known a resin optical waveguide utilizing an adiabatic-coupling as a waveguide for transmitting optical signals between a silicon optical waveguide formed in an optical integrated circuit and an optical fiber (e.g., refer to Patent Document 1). In the case where such a resin optical waveguide is used, propagation loss between the silicon optical waveguide and the optical fiber can be reduced.